When industrial-rated circuit breakers are double-branch-connected within lighting panelboard assemblies, the line ends of opposing pairs of circuit breakers are arranged close together within the panelboard enclosure. For purposes of this disclosure, "double-branch" connection is defined as that arrangement whereby a pair of circuit breakers are connected to the same phase bus bars. The line terminal lugs are omitted and the circuit breaker line straps are connected with the bus bars by means of offset branch strap connectors.
The old style circuit breakers were open at the top of the line lug compartments to facilitate the insertion of a tool to connect the circuit breaker line terminal lugs within a multi-phase power distribution circuit. With newer designs, a cap is arranged over the line terminal compartments once the terminal connections were made to prevent inadvertent contact with the bus bars or line straps per se.
When an overcurrent condition occurs, the gases originating within one of the closely aligned circuit breakers could transfer to the other circuit breaker within the double-branch arrangement, resulting in a phase-to-phase fault.
To prevent the occurrence of such phase-to phase faults within prior art panelboards, a fiberboard barrier is inserted to prevent the exhaust gases from one of the circuit breakers from entering the line lug compartments of the opposing circuit breaker. Over long periods of continuous use, the fiber material could become brittle and deteriorate. Another problem with the fiberboard barriers suggested by the prior art, is the removal of the barrier for access to the line terminals and the subsequent connection of the circuit breakers to the line terminal straps without replacing the barrier.
One purpose of this invention is to provide an effective exhaust gas barrier that allows the circuit breakers to be connected to the line straps and removed from the line straps without first having to remove the exhaust gas barrier.